feat: implement WebCodecs Opus decode for browser listen

- Add broadcastOpusToWeb to PcmBroadcaster interface for raw Opus packets
- Server broadcasts Opus frames with mode byte (1) + user hash + packet data
- Browser detects packet mode: mode=1 for Opus, mode=0 for legacy PCM
- Implement WebCodecs AudioDecoder for Opus decoding in browser
- Keep existing PCM playback as fallback for compatibility
- Show error if WebCodecs unsupported
- Fixes listen feature under Bun where native Opus decode unavailable

src/recorder.ts

@@ -176,6 +176,7 @@ export async function startRecording(
         onPacket: (chunk) => {
           if (chunk.length < 8) return;
           segmentManager.rotateIfNeeded(oggPacketStream);
+          broadcaster.broadcastOpusToWeb?.(chunk, userId);
           if (!broadcaster.broadcastPcmToWeb) return;
           decoder.rotateIfNeeded();
           decoder.write(chunk);